A field trip to Posina catchment

Since a couple of years we started to work on modelling Posina catchment in the Italian pre-alpine area. There University of Padua colleagues, Marco Borga heading the group, started hydrological measurements since many years. Posina is a small catchment (116 km$^{2}$) located in the Alpine foothills of the Veneto Region in Italy. The elevation difference of the basin is 1820 meters. The climate is characterised as wet, with annual precipitation of 1,645 mm and annual runoff of 1000 mm. For a detailed report on its hydrological budget please see Abera's et al. paper.
Finally we had the occasion to visit it with Marco Borga himself and Giulia Zuecco on March 22 afternoon. Please here below find a photographic synthesis with  some comment.

1 - The position of the gauge station at the Stancari outlet.

2 - A view of the position of Bazzoni gauge position.

3 - A view of the Ressi sub-catchment top with a few of the buckets

4 -A more panoramic view (was not a sunny day)

5 - A panorama view with Giulia, Marco and Marialaura from left to right.

6 - Going inside the catchment, to explore these channels (?) or hollow. Soil depth is not very large here. Many trees just did not succeeded to stay still due to the limited roots development. Here and there the bedrock outcrops, but in other position, especially in the concave parts, soil seems to be deeper. 

7 - Here the bedrock channel is visible. We can see also the soil section with the roots of the tree in the foreground.

8 - The V-shaped weir where discharge and water level is measured

9 - The water sampler to do isotopes estimations

10 - A view of the sampler - weir area from below. Please observe the big fallen tree that just slightly touched the box with the sampler when falling. 

11- The throughfall measurement site. 500 hundred buckets for 500 hundred square meters

12 - The stemflow measurements 

It was a nice a pleasant trip! We hope to continue the collaboration further. 

Marco Borga's talk

Marco concentrated mainly on the interplay between rainfall and the catchment structure, as derived from the data of his Hydrate EU project. Interestingly he introduced (after, he said, initial suggestions from Jim Smith) some spatial moments (i.e. the moments of the spatial distribution of the rainfall with respect to the catchment) to quantify the storm movements during flood events. His results shows that usually storm can be considered almost stationary (on average) over the catchments, but some events are more strongly characterized than other, and especially, concentrating close to the mountain ridge. This cannot be obviously a general result, since around the World the relative position of the relative location of storm to the catchment can be different. What is of general importance is that the space-time evolution of storms can be of some relevance in producing flash floods, and that now we have a statistical tool for quantifying these storms.

 Here it is Marco's abstract on his seminar: Spatial moments of catchment rainfall: rainfall spatial organisation, basin morphology and flood response

 "In this talk I will introduce a general analytical framework for assessing the dependence existing between spatial rainfall organisation, basin morphology and runoff response. The analytical framework builds upon a set of spatial rainfall statistics (termed ‘spatial moments of catchment rainfall’) which describe the spatial rainfall organisation in terms of concentration and dispersion statistics as a function of the distance measured along the flow routing coordinate. The introduction of these statistics permits derivation of a simple relationship for the quantification of storm velocity at the catchment scale. The talk illustrates the development of the analytical framework and explains the conceptual meaning of the statistics by means of application to five extreme flash floods occurred in various European regions in the period 2002-2007. High resolution radar rainfall fields and a distributed hydrologic model are employed to examine how effective are these statistics in describing the degree of spatial rainfall organisation which is important for runoff modelling. This is obtained by quantifying the effects of neglecting the spatial rainfall variability on flood modelling, with a focus on runoff timing. The size of the study catchments ranges between 36 to 982 km2. The analysis reported here shows that the spatial moments of catchment rainfall can be effectively employed to isolate and describe the features of rainfall spatial organization which have significant impact on runoff simulation. These statistics provide essential information on what space–time scales rainfall has to be monitored, given certain catchment and flood characteristics, and what are the effects of space–time aggregation on flood response modeling."